.\" $OpenBSD: X509v3_addr_add_inherit.3,v 1.11 2023/10/01 22:46:21 tb Exp $
.\"
.\" Copyright (c) 2023 Theo Buehler <tb@openbsd.org>
.\"
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.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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.Dd $Mdocdate: October 1 2023 $
.Dt X509V3_ADDR_ADD_INHERIT 3
.Os
.Sh NAME
.Nm X509v3_addr_add_inherit ,
.Nm X509v3_addr_add_prefix ,
.Nm X509v3_addr_add_range ,
.Nm X509v3_addr_canonize ,
.Nm X509v3_addr_is_canonical
.Nd RFC 3779 IP address delegation extensions
.Sh SYNOPSIS
.In openssl/x509v3.h
.Ft int
.Fo X509v3_addr_add_inherit
.Fa "IPAddrBlocks *addrblocks"
.Fa "const unsigned afi"
.Fa "const unsigned *safi"
.Fc
.Ft int
.Fo X509v3_addr_add_prefix
.Fa "IPAddrBlocks *addrblocks"
.Fa "const unsigned afi"
.Fa "const unsigned *safi"
.Fa "unsigned char *prefix"
.Fa "const int prefixlen"
.Fc
.Ft int
.Fo X509v3_addr_add_range
.Fa "IPAddrBlocks *addrblocks"
.Fa "const unsigned afi"
.Fa "const unsigned *safi"
.Fa "unsigned char *min"
.Fa "unsigned char *max"
.Fc
.Ft int
.Fo X509v3_addr_canonize
.Fa "IPAddrBlocks *addrblocks"
.Fc
.Ft int
.Fo X509v3_addr_is_canonical
.Fa "IPAddrBlocks *addrblocks"
.Fc
.Sh DESCRIPTION
An
.Vt IPAddrBlocks
object represents the content of
an IP address delegation extension
as defined in RFC 3779, section 2.2.3.1.
It holds lists of IP address prefixes and IP address ranges
delegated from the issuer to the subject of the certificate.
It can be instantiated as explained in the EXAMPLES section
and its internals are documented in
.Xr IPAddressRange_new 3 .
.Pp
Each list in a well-formed
.Vt IPAddrBlocks
object is uniquely identified by
an address family identifier (AFI) and
an optional subsequent address family identifier (SAFI).
Lists can be absent or can contain an
.Dq inherit
marker to indicate that the resources are to be inherited
from the corresponding list of the issuer certificate.
.Pp
Per specification, an AFI is an unsigned 16-bit integer and
a SAFI is an unsigned 8-bit integer.
For IPv4 and IPv6 there are the predefined constants
.Dv IANA_AFI_IPV4
and
.Dv IANA_AFI_IPV6 ,
which should be the only values used for
.Fa afi
in this API.
In practice,
.Fa safi
is always NULL.
.Fa afi
is generally silently truncated to its lowest 16 bits and, if
.Fa safi
is non-NULL,
only the lowest 8 bits of the value pointed at are used.
.Pp
.Fn X509v3_addr_add_inherit
adds a list with an
.Dq inherit
marker to
.Fa addrblocks .
If a list corresponding to
.Fa afi
and
.Fa safi
already exists, no action occurs if it is marked
.Dq inherit ,
otherwise the call fails.
.Pp
.Fn X509v3_addr_add_prefix
adds a newly allocated internal representation of the
.Fa prefix
of length
.Fa prefixlen
to the list corresponding to
.Fa afi
and the optional
.Fa safi
in
.Fa addrblocks .
If no such list exists, it is created first.
If the list exists and is marked
.Dq inherit ,
the call fails.
.Fa prefix
is expected to be a byte array in network byte order.
It should point at enough memory to accommodate
.Fa prefixlen
bits and it is recommended that all the bits not covered by the
.Fa prefixlen
be set to 0.
It is the caller's responsibility to ensure that the
.Fa prefix
has no address in common with any of
the prefixes or ranges already in the list.
If
.Fa afi
is
.Dv IANA_AFI_IPV4 ,
.Fa prefixlen
should be between 0 and 32 (inclusive) and if
.Fa afi
is
.Dv IANA_AFI_IPV6 ,
.Fa prefixlen
should be between 0 and 128 (inclusive).
.Pp
.Fn X509v3_addr_add_range
is similar to
.Fn X509v3_addr_add_prefix
for the closed interval of IP addresses between
.Fa min
and
.Fa max
in network presentation.
If
.Fa afi
is
.Dv IANA_AFI_IPV4 ,
.Fa min
and
.Fa max
should point at 4 bytes of memory
and if
.Fa afi
is
.Dv IANA_AFI_IPV6 ,
.Fa min
and
.Fa max
should point at 16 bytes of memory.
In case the range of IP addresses between
.Fa min
and
.Fa max
is a prefix, a prefix will be added instead of a range.
It is the caller's responsibility to ensure that
.Fa min
is less than or equal to
.Fa max
and that it does not contain any address already present
in the list.
Failure to do so will result in a subsequent failure of
.Fn X509v3_addr_canonize .
.Pp
.Fn X509v3_addr_canonize
attempts to bring the
.Pf non- Dv NULL
.Fa addrblocks
into canonical form.
An
.Vt IPAddrBlocks
object is said to be in canonical form if it conforms
to the ordering specified in RFC 3779:
section 2.2.3.3 requires that
the list of lists be sorted first by increasing
.Fa afi
and then by increasing
.Fa safi ,
where NULL is the minimal SAFI;
section 2.2.3.6 requires that each list be in minimal form and sorted.
The minimality requirement is that all adjacent prefixes
and ranges must be merged into a single range and that each
range must be expressed as a prefix, if possible.
In particular, any given address can be in at most one list entry.
The order is by increasing minimal IP address in network byte order.
.Pp
.Fn X509v3_addr_is_canonical
indicates whether
.Fa addrblocks
is in canonical form.
.Sh RETURN VALUES
All these functions return 1 on success and 0 on failure.
Memory allocation failure is one possible reason for all of them.
Sometimes an error code can be obtained by
.Xr ERR_get_error 3 .
.Pp
.Fn X509v3_addr_add_inherit
fails if the list corresponding to
.Fa afi
and the optional
.Fa safi
already exists and is not marked
.Dq inherit .
.Pp
.Fn X509v3_addr_add_prefix
and
.Fn X509v3_addr_add_range
fail if a list corresponding to
.Fa afi
and the optional
.Fa safi
already exists and is marked
.Dq inherit ,
or if
.Fa prefixlen
is outside the interval [0,32] for IPv4 addresses
or [0,128] for IPv6 addresses.
.Pp
.Fn X509v3_addr_canonize
fails if one of the lists in
.Fa addrblocks
is malformed,
in particular if it contains corrupt, overlapping,
or duplicate entries.
Corruption includes ranges where
.Fa max
is strictly smaller than
.Fa min .
The error conditions are generally indistinguishable.
.Pp
.Fn X509v3_addr_is_canonical
returns 1 if
.Fa addrblocks
is in canonical form.
A return value of 0 can indicate non-canonical form or a corrupted list.
.Sh EXAMPLES
Construct the first extension from RFC 3779, Appendix B.
.Bd -literal
#include <sys/socket.h>
#include <arpa/inet.h>

#include <err.h>
#include <stdio.h>
#include <unistd.h>

#include <openssl/asn1.h>
#include <openssl/objects.h>
#include <openssl/x509.h>
#include <openssl/x509v3.h>

const char *prefixes[] = {
	"10.0.32/20", "10.0.64/24", "10.1/16",
	"10.2.48/20", "10.2.64/24", "10.3/16",
};
#define N_PREFIXES (sizeof(prefixes) / sizeof(prefixes[0]))

static void
hexdump(const unsigned char *buf, size_t len)
{
	size_t i;

	for (i = 1; i <= len; i++)
		printf(" 0x%02x,%s", buf[i \- 1], i % 8 ? "" : "\en");
	if (len % 8)
		printf("\en");
}

int
main(void)
{
	IPAddrBlocks *addrblocks;
	X509_EXTENSION *ext;
	unsigned char *der;
	int der_len;
	size_t i;

	if (pledge("stdio", NULL) == \-1)
		err(1, "pledge");

	/*
	 * Somebody forgot to implement IPAddrBlocks_new().  IPAddrBlocks
	 * is the same as STACK_OF(IPAddressFamily).  As such, it should
	 * have IPAddressFamily_cmp() as its comparison function.  It is
	 * not possible to call sk_new(3) because IPAddressFamily_cmp()
	 * is not part of the public API.  The correct comparison function
	 * can be installed as a side-effect of X509v3_addr_canonize(3).
	 */
	if ((addrblocks = sk_IPAddressFamily_new_null()) == NULL)
		err(1, "sk_IPAddressFamily_new_null");
	if (!X509v3_addr_canonize(addrblocks))
		errx(1, "X509v3_addr_canonize");

	/* Add the prefixes as IPv4 unicast. */
	for (i = 0; i < N_PREFIXES; i++) {
		unsigned char addr[16] = {0};
		int len;
		int unicast = 1; /* SAFI for unicast forwarding. */

		len = inet_net_pton(AF_INET, prefixes[i], addr,
		    sizeof(addr));
		if (len == \-1)
			errx(1, "inet_net_pton(%s)", prefixes[i]);
		if (!X509v3_addr_add_prefix(addrblocks, IANA_AFI_IPV4,
		    &unicast, addr, len))
			errx(1, "X509v3_addr_add_prefix(%s)", prefixes[i]);
	}
	if (!X509v3_addr_add_inherit(addrblocks, IANA_AFI_IPV6, NULL))
		errx(1, "X509v3_addr_add_inherit");

	/*
	 * Ensure the extension is in canonical form.  Otherwise the two
	 * adjacent prefixes 10.2.48/20 and 10.2.64/24 are not merged into
	 * the range 10.2.48.0--10.2.64.255.  This results in invalid DER
	 * encoding from X509V3_EXT_i2d(3) and i2d_X509_EXTENSION(3).
	 */
	if (!X509v3_addr_canonize(addrblocks))
		errx(1, "X509v3_addr_canonize");

	/* Create the extension with the correct OID; mark it critical. */
	ext = X509V3_EXT_i2d(NID_sbgp_ipAddrBlock, 1, addrblocks);
	if (ext == NULL)
		errx(1, "X509V3_EXT_i2d");

	der = NULL;
	if ((der_len = i2d_X509_EXTENSION(ext, &der)) <= 0)
		errx(1, "i2d_X509_EXTENSION");

	hexdump(der, der_len);

	/* One way of implementing IPAddrBlocks_free(). */
	sk_IPAddressFamily_pop_free(addrblocks, IPAddressFamily_free);
	X509_EXTENSION_free(ext);
	free(der);

	return 0;
}
.Ed
.Pp
Implement the missing public API
.Fn d2i_IPAddrBlocks
and
.Fn i2d_IPAddrBlocks
using
.Xr ASN1_item_d2i 3 :
.Bd -literal
IPAddrBlocks *
d2i_IPAddrBlocks(IPAddrBlocks **addrblocks, const unsigned char **in,
    long len)
{
	const X509V3_EXT_METHOD *v3_addr;

	if ((v3_addr = X509V3_EXT_get_nid(NID_sbgp_ipAddrBlock)) == NULL)
		return NULL;
	return (IPAddrBlocks *)ASN1_item_d2i((ASN1_VALUE **)addrblocks,
	    in, len, ASN1_ITEM_ptr(v3_addr\->it));
}

int
i2d_IPAddrBlocks(IPAddrBlocks *addrblocks, unsigned char **out)
{
	const X509V3_EXT_METHOD *v3_addr;

	if ((v3_addr = X509V3_EXT_get_nid(NID_sbgp_ipAddrBlock)) == NULL)
		return \-1;
	return ASN1_item_i2d((ASN1_VALUE *)addrblocks, out,
	    ASN1_ITEM_ptr(v3_addr\->it));
}
.Ed
.Pp
The use of the undocumented macro
.Dv ASN1_ITEM_ptr()
is necessary if compatibility with modern versions of other implementations
is desired.
.Sh SEE ALSO
.Xr ASIdentifiers_new 3 ,
.Xr crypto 3 ,
.Xr inet_net_ntop 3 ,
.Xr inet_ntop 3 ,
.Xr IPAddressRange_new 3 ,
.Xr X509_new 3 ,
.Xr X509v3_addr_get_range 3 ,
.Xr X509v3_addr_validate_path 3 ,
.Xr X509v3_asid_add_id_or_range 3
.Sh STANDARDS
RFC 3779: X.509 Extensions for IP Addresses and AS Identifiers:
.Bl -dash -compact
.It
section 2: IP Address delegation extension
.El
.Pp
RFC 7020: The Internet Numbers Registry System
.Pp
RFC 7249: Internet Number Registries
.Pp
.Rs
.%T Address Family Numbers
.%U https://www.iana.org/assignments/address\-family\-numbers
.Re
.Pp
.Rs
.%T Subsequent Address Family Identifiers (SAFI) Parameters
.%U https://www.iana.org/assignments/safi\-namespace
.Re
.Sh HISTORY
These functions first appeared in OpenSSL 0.9.8e
and have been available since
.Ox 7.1 .
.Sh BUGS
.Fn IPAddrBlocks_new ,
.Fn IPAddrBlocks_free ,
.Fn d2i_IPAddrBlocks ,
and
.Fn i2d_IPAddrBlocks
do not exist and
.Fa IPAddrBlocks_it
is not public.
The above examples show how to implement the four missing functions
with public API.
.Pp
.Fn X509v3_addr_add_range
should check for inverted range bounds and overlaps
on insertion and fail instead of creating a nonsensical
.Fa addrblocks
that fails to be canonized by
.Fn X509v3_addr_canonize .
.Pp
If
.Dv NULL
is passed to
.Xr X509v3_asid_canonize 3 ,
it succeeds.
.Fn X509v3_addr_is_canonical
considers
.Dv NULL
to be a canonical
.Vt IPAddrBlocks .
In contrast,
.Fn X509v3_addr_canonize
crashes with a
.Dv NULL
dereference.
.Pp
The code only supports the IPv4 and IPv6 AFIs.
This is not consistently enforced across implementations.
.Pp
.Fn X509v3_addr_add_range
fails to clear the unused bits set to 1 in the last octet of
the
.Vt ASN1_BIT_STRING
representation of
.Fa max .
This confuses some software.
